The human foot is a very complex biological mechanism. While walking the load on the foot at heel strike is typically about one and a half times a person's body weight. When running or carrying extra weight, such as a backpack, loads on the foot may exceed three times the body weight. The many bones, muscles, ligaments, and tendons of the foot function to absorb and dissipate the forces of impact, carry the weight of the body and other loads, and provide forces for propulsion. Properly designed shoe insoles can assist the foot in performing these functions and protect the foot from injury.
Insoles may be custom made to address the specific needs of an individual. They may be made based on casts of the end user's foot or may be made of a thermoplastic material that is molded to the contours of the end user's foot. However, it is not practical to make such insoles for the general public. Like most custom made items, custom insoles tend to be expensive because of the low volume and extensive time needed to make and fit them properly.
To be practical for distribution to the general public, an insole must be able to provide benefit to the user without requiring individualized adjustment and fitting. A first type of insole commonly available over-the-counter emphasizes cushioning the foot so as to maximize shock absorption. For typical individuals cushioning insoles perform adequately while engaged in light to moderate activities such as walking or running. That is, a cushioning insole provides sufficient cushioning and support for such activities.
However, for more strenuous or technically challenging activities, such as carrying a heavy backpack or traversing difficult terrain, a typical cushioning insole may not be adequate. Under such conditions, a cushioning insole by itself would not provide enough support and control, and may tend to bottom out during use.
Another type of over-the-counter insole emphasizes control. Typically, such insoles are made to be relatively stiff and rigid so as to control the bending and twisting of the foot by limiting foot motion. The rigid structure is good at controlling motion, but is not very forgiving. As a result, when motion of the foot reaches a limit imposed by the rigid structure, the load on the foot tends to change abruptly and may increase the load on the structures of the foot. Because biological tissues such as tendons and ligaments are sensitive to the rate at which they are loaded, the abrupt change in load may cause injury or damage.
In view of the foregoing, it would be desirable to provide an over-the-counter insole that provides both cushioning and control.
It would also be desirable to provide an insole that provides both cushioning and control and is practical for use by the general public.